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Thread: Digital Volume control

  1. #1
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    Digital Volume control

    Is it bad?
    Of course it is, it is digital so reduced dynamics and lack of resolution is what you get.
    This is at least what the audiophile community says.
    But is it true?

    Mark Mallinson provided some data comparing analog and digital volume control using 16-bit audio

    Level/ Analog /Digital
    0 96 96
    -5 96 96
    -10 96 94
    -15 96 89
    -20 96 84
    -25 96 79
    -30 96 74
    -35 96 69
    -40 96 64
    -45 91 59
    -50 86 54
    -55 81 49
    -60 76 44
    S/N ratio of volume control using a DAC with a -104dB S/N ratio.

    Indeed pretty soon (-10 dBFS) a digital volume control gives a worse S/N ratio compared with analog.

    Level /Analog /Digital
    0 96 96
    -5 96 96
    -10 96 96
    -15 96 96
    -20 96 96
    -25 96 96
    -30 96 96
    -35 96 96
    -40 96 92
    -45 91 87
    -50 86 82
    -55 81 77
    -60 76 72
    S/N ratio of volume control using a DAC with a -132dB S/N ratio.

    Obvious if a DAC is whisper quit, the difference is less dramatic.
    But DACs with a -132dB S/N ratio are rare.
    A bit more: http://www.6moons.com/audioreviews/resonessence/2.html

  2. #2
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    Interesting analysis. Thanks for posting it Vince. Is there more to how the figures where computed?

  3. #3
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    Unfortunately not.
    I must admit I’m a bit surprised.
    I didn’t expect such a profound difference.

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    Member Sponsor [Technical Expert] DonH50's Avatar
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    Not all digital volume controls work that way and thus do not exhibit as much degradation. Just reducing the bits in the DAC to reduce the volume is reducing resolution, hurting SNR. Some designs are "hybrid", using a DAC to control the bias or set the gain in a volume control circuit without such a huge hit.

    That said, I have no idea what, or even how to find out, what sort of control is in a given component. Amir, you could measure it with your AP unit...
    Don Herman
    "After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
    Don's Technical Articles on WBF

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    It would make a good test. I will put it on my todo list.

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    Frankly, all this talk about things like 104 vs 132dB S/N ratio is just ridiculous. By the time you hit 60dB down you're getting close to the limit of what you can actually pick up over speakers without concentrating pretty hard.

    Get a fragment of a conventional piece of classical music and create a CD of the original, and then successivefully follow that track with other tracks of copies of the original attenuated, cut in volume, by 20dB, 40dB, 60dB, 80dB, 100dB. Play the CD at the volume you would normally use to listen to the original, the first, track, as if in a listening session. Then do NOT touch the volume control! If you can hear anything of the 80dB version from your normal listening position then you've got some pretty amazing ears!!

    Frank

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    Quote Originally Posted by Vincent Kars View Post
    Indeed pretty soon (-10 dBFS) a digital volume control gives a worse S/N ratio compared with analog.
    S/N is not relevant in this discussion. Consider the usual cases where S/N is of concern: An audio recording is delivered by various formats: CD, FM radio, audio tape, cassette. The signal would be played at the same loudness each time, but the noise levels would vary from inaudible to very audible.

    In the case of the analog volume control, assuming a noiseless output stage and power amp, the signal and the noise both reduce together as the volume is turned down. If the source was noiseless at full volume, it remains noiseless as volume is reduced.

    So what about the digital volume control? The DAC has a noise floor which presumably reflects the result of a properly dithered signal. If the DAC is worth its salt when playing at full volume, the noise is acceptably low, probably inaudible except in unusually quiet rooms. Furthermore, since it is properly dithered, there is no quantization noise when signals are present, no matter how softly they are recorded.

    Now we turn down the volume digitally, as much as you like, 10dB, 40 dB. The noise floor remains fixed, i.e., virtually inaudible. The quantization noise remains non-existent as it is still properly dithered.

    S/N has reduced, but this time the noise is constant while the signal is reduced. Where's the problem?

  8. #8
    Welcome to WBF, Roger.

    Tim
    In high-end audio, you can't even fight an opinion with the facts.

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    VIP/Donor [VIP/Donor] microstrip's Avatar
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    The main concern of a pure digital volume control in consumer products is that it has to cover a much large dynamic range than considered in the table - say 60 dB useful range, 15dB for variation of amplifier sensitivity , 20 dB for speaker sensitivity and perhaps 6 dB for room effects. If a complementary system based on variable analog gain matching is needed for coarse matching, why not use it to fully control volume?

  10. #10
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    Found the paper by Resonessence Labs, but no new information
    http://www.resonessencelabs.com/invi...tal_volume.pdf

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